NBSIR 73-167

Fire Endurance Test of a

Roof/Ceiling Construction of Paper

Honeycomb and Gypsum Board

B. C. Son

Center for Building Technology

Institute for Applied Technology

National Bureau of Standards

Washington, D. C. 20234

January 1973

Final Report

Prepared for Office of Research and Technology

Department of Housing and Urban Development

Washington. D. C. 20234

NBSIR 73-167

FIRE ENDURANCE TEST OF A

ROOF/CEILING CONSTRUCTION OF PAPER

HONEYCOMB AND GYPSUM 30ARD

B. C. Son

Center for Building Teclinology

Institute for Applied Technology

National Bureau of Standards

Washington, D. C. 20234

January 1973

Final Report

Prepared for • Office of Research and Technology

Department of Housing and Urban Development

Washington, D. C. 20234

U. S. DEPARTMENT OF COMMERCE, Frederick B. Dent, Secretary

NATIONAL BUREAU OF STANDARDS, Richard W. Roberts, Director
I
Fire Endurance Test of a Roof/Ceiling

Construction of Paper Honeycomb and Gypsum Board

by

B. C. Son

Building Fires and Safety Section

Center for Building Technology

ABSTRACT

In a program of evaluation of various housing systems proposed under

Operation BREAKTHROUGH, a fire endurance test was performed at the

National Bureau of Standards on a roof /ceiling assembly consisting of a

paper honeycomb structural core surfaced on both sides with glass-fabric

impregnated with polyester resin and outer layers of gypsum board.

The test method was generally in accordance with the requirements

of ASTM E 119, Fire Tests of Building Construction and Materials, for

loadbearing roof assemblies. The applied load was 15.9 psf and the test

results are valid only for roof /ceilings of similar construction loaded

at or below the stress level developed by this loading.

Under the loading of 15.9 psf on a 13 ft. 5 in. span, which produced

a stress equivalent to the application of 20 psf on a 12 ft. span,

failure occurred by flame-through Of the roof /ceiling assembly at 37

min. 13 sec.

Key Words: Fire endurance; fire test; flame- through failure, structural

panel; glass-fabric reinforced plastic; housing systems;

Operation BREAKTHROUGH; paper honeycomb; roof /ceiling assembly;

structural panel

1
TABLE OF CONTENTS

Page

ABSTRACT i

1.0 Introduction 1

2.0 Description of Test Specimen 1

3.0 Test Method and Instrumentation 2

4.0 Test Evaluation 4

5.0 Results of Test 4

6.0 Discussion of Results 5

TABLE I Log of Test Observations 7

APPENDIX SI Conversion Units 8

ii
1.0 INTRODUCTION

A sandwich panel roof /ceiling assembly designed for single family

attached housing was submitted for a fire endurance test at the National

Bureau of Standards under the Operation BREAKTHROUGH program conducted

for the Department of Housing and Urban Development. The test was run

generally in accordance with the requirements of the Standard Methods of

Fire Tests of Building Construction and Materials, ASTM E 119—^.

The assembly panels consisted of paper honeycomb cores surfaced on

both sides with glass-fabric impregnated with polyester resin and gypsum

board covers. The exterior (top) side of the panels had an additional

weather-resistant surfacing. The panels were unframed except for closeout

pieces at the edges.

2.0 DESCRIPTION OF TEST SPECIMEN

The roof /ceiling assembly, as shown in figure 1, consisted of two

panels of equal size, each 13 ft. 5 in. by 8 ft. 11 in., butted on the

long side to fit in the NBS floor test furnace.

The panels consisted of 6 in. thick f lame-retardant treated paper

honeycomb cores with woven glass fiber roving and polyester resin facings

bonded to both sides of the core. Type X gypsum board, 5/8 in. thick,

was applied to the resin facings with a polyester adhesive reinforced with

one percent asbestos fiber. The joints in the boards on the two sides

of a panel were staggered. The vreather-resistant coating applied to the

gypsum board on the exterior side of the panels consisted of a resin with

—^ Standard Methods of Fire Tests of Building Construction and Materials , American Society for Testing and Materials Designation E 119-71, available

at 1916 Race Street, Philadelphia, Pa. 19103.

1
chopped glass fiber and sand. The joints between the gypsum boards on

the surface of the panels were taped and filled with plaster joint compound.

The honeycomb core was stopped 3 in. from the long edges of each

panel to allow for finishing with four layers of 3/4 in. plywood, laminated to form a 3 in. by 6 in. section. Although the panels were ostensibly unframed, these plywood closures in effect provided 3 in. by 6 in.

beams at the extreme ends of the test specimen and a 6 in. by 6 in. beam

at its center. The exposed side of the joint at the specimen center,

between the panels, was covered with a 5 in. wide strip of 5/8 in. gypsum

board. v

With the panels installed the clearance between the panel edges

and the furnace walls was 1/2 to 1 in. These spaces were closed by the

furnace flanges which supported the test structure on its perimeter and

by mineral wool stuffing.

3.0 TEST METHOD AND INSTRUMENTATION

The roof /ceiling assembly, tested in the NBS floor furnace, was exposed on its underside to a fire controlled to give an average temperature

in the furnace in accordance with the time-temperature curve of the ASTM

E 119 standard. Figure 2 is a section of the floor-test furnace with

typical specimen in place.

The temperature within the furnace was determined from the readings

of 12 protected thermocouples symmetrical distributed in the chamber.

To determine the temperatures on the unexposed surface of the

specimen, nine Chromel-Alumel (type K) thermocouples were located

in a symmetrical pattern over the two panels, four away from the joint

2
on each panel and one at the center over the joint (locations shown

in figure 1) . Each thermocouple was covered with a standard asbestos

pad (6 by 6 by 0.4 in.) as specified in the ASTM E 119 standard.

Additionally, three thermocouples were placed in the core within each

panel. Temperature readings indicated by all the thermocouples, including those in the furnace, were recorded at 1-minute intervals on

a data logger and later processed and plotted by computer.

Vertical deflections of the panels during the test were measured

at three points on the longitudinal center line, at the midpoint over

the joint and at either quarter point. Indication of movement was by

pointers on wires attached to the three check points. The wires, held

taut by weights, passed over pulleys which in turn were connected to

linear deflection potentiometers.

Conventional roof design live loading on a structure for which the

panels under test are intended was taken as 20 psf. The panels are normally manufactured in 12 ft. widths. The 13 ft. 5 in. wide specimens of

this test were made specially to conform to the size of the NBS floor

furnace. A load of 15.9 psf was applied to the test specimen to provide

a bending moment in the wider panels equivalent to that produced by 20

psf loading on a 12 ft. span. Applied symmetrically at 36 points by

means of 6 by 24 in. channels, the load was approximately uniform over

the entire surface. Although the load was applied 24 hours before the

start of the fire endurance test no significant creep deflection was

observed.

3
4.0 TEST EVALUATION

The fire endurance of a roof/ceiling structure according to ASTM

E 119 is the time required to reach the first occurrence of the following

criteria of failure:

1. Inability to sustain the applied load.

2. Passage of flame or gas, through the structure to the unexposed

surface, hot enough to ignite cotton waste.

3. A temperature rise of 250'F (139°C) average, or 325°F

(181° C) at one point above the initial temperature on

the unexposed surface.

5.0 RESULTS OF TEST

Failure occurred at an observed time of 37 min. 50 sec. by flamethrough at the unexposed surface through a joint in the gypsum boards of

one of the panels. A local load failure occurred about 10 sec. later at

the site of the flame penetration.

Since, as indicated by figure 2, the average temperature in the

furnace (figure 2) was slightly below that provided by the standard timetemperature curve, the time to failure was corrected to 37 min. 13 sec.

,

by the correction formula in ASTM E 119.

At the time of failure, the average temperature of the unexposed

surface was 136°F (58°C) , the maximum at one point 182°F(83°C), indicating that the initial flame-through did not occur in the immediate

vicinity of any of the thermocouples. Temperatures at the six thermocouples inside the panel show suddenly accelerated rises at times

corresponding to the falling of the ceiling gypsum boards (30 min.).

4
Time-temperature curves for the thermocouples on the unexposed surface

are shown in figure 4; those in the paper core, in figure 5. The flamethrough failure and the inability to sustain the load at the failure

point are illustrated in figure 6.

The rate of measured deflection on the panels was slow until about

30 min. of the test and after that time the rate of the deflection

increased slightly at the two quarter points. There was no significant

deflection at the center point at any time. Figure 7 shows the deflection

at the two quarter points.

A log of test observations is given in the Appendix.

6.0 DISCUSSION OF RESULTS

The local distintegration of the gypsum board under one of the loading members probably accelerated bv the burnout of the supporting core,

provided the opening for the initial breakthrough of flame to cause

failure. Effects of the fire exposure on the underside of the specimen

can be seen in figures 8 and 9.

Absence of deflection at the center of the roof /ceiling panel can

be attributed to the support provided by the closeout pieces at the edges

of the two panels making up the assembly. These laminated plywood beams,

with load carrying capacity far in excess of the total applied to the

structure, were not only protected from the fire by the gypsum board

ceiling .beneath, but in themselves over the time period of this test,

would maintain a considerable capacity to sustain load even if fully

exposed to the fire. It should be noted that in actual construction

the closeout pieces, even if comparable in size and material, would probably not be supplied in the close spacing used in the test specimen.

5
The applied load of 15.9 psf in this test, corresponded to a 20 psf

live load on a 12 ft. span. Therefore, the results of this test are

applicable only to similar roof /ceiling structures with spans and loads

developing a bending moment not exceeding that developed in the structure

tested.

The flame retardant treatment said to have been applied to the paper

honeycomb core apparently did little or nothing to prevent its destruction

when exposed to fire. After test, the paper honeycomb core continued to

smolder for several hours with occasional eruption Into open flaming.

Figure 10 shows flaming of the core material two hours after application

of a water spray from a fog nozzle at the conclusion of the fire exposure.

6

it
TABLE I

Log of Test Observations

TIME OBSERVATIONS

inin:sec

0:00 Start of test.

2:00 Blue flame over the exposed surface.

3:00 Flame subsided.

4:00 Blue flame again spreading over the exposed surface.

4:20 Flame not apparent. Much smoke coming through the

unexposed surface.

24:00 Flaming at a gypsum joint near south* quarter point on exposed surface (honeycomb core appears to be burning).

28:00 Large flaming at the middle of the south panel on exposed

surface (opening up of the gypsum joints)

.

30:00 Bottom layer of gypsum board on south panel has started to

fall into the furnace.

30:50 Furnace filling with smoke and flame. Deflection of 1-in.

at the south quarter point was observed on the recorder.

35:00 A gypsum joint near and to the south of the center on the

unexposed surface started to open and the gypsum board under

a nearby loading point was being crushed.

37:50 Flame-through occurring at the point where the gypsum board

was failing under a loading point (see Figure 6)

.

38:00 Pieces of the upper layer of gypsum board at this loading

point falling into the furnace (a local load failure)

.

39:00 Gas off, end of test.

* To identify the location of an occurrence, the two ends of the assembly

are differentiated according to their orientation.

7
APPENDIX I

SI Conversion Units

In view of present accepted practice in this country in this

technological area, common US units of measurement have been used

throughout this paper. In recognition of the position of the United

States as a signatory to the General Conference on Weights and Measurements which gave official status to the metric SI system of units in

1960, we assist readings interested in making use of the coherent system

of SI units by giving conversion factors applicable to US units used

in this paper.

Length

1 in = 0.0254 meter

1 ft ^ 0.3048 meter

Mas s

1 pound = 0.45 kilograms

Force

1 kip 4448 newton

Stress

1 psf 47.88 newton/meters"

Temperature

Temperature in °F = 9/5 (Temperature in °C) + 32°F

8

10
IUUU_|

TIME (MINUTES)

Figure 3. AVERAGE FURNACE TEMPERATURE FOR TEST 482 COMPARED WITH STANDARD El 19.

TIME (MINUTES)

Figuie 4. MAXIMUM AND AVERAGE SURFACE TEMPERATURE RISE FOR TEST 482

11
1000-,

800_

600_

400_

200_

0

(See Fig 1 for the corresponding locations of thermocouples)

Symbols Location

0 Top of paper honeycomb in north panel

X Middle of paper honeycomb

north panel

Bottom of paper honeycomb in / T ] north panel

Top of paper honeycomb in

south panel

1- Middle of paper honeycomb

in south panel

Bottom of paper honeycomb

in south panel

0 5 10 Is So Ss AO

„. ^ TIME (MINUTES) Figure 5.

TEMPERATURE RISES AT SIX THERMOCOUPLES WITHIN ROOF- CEILING ASSEMBLY.

12

45
Figure 6. Flame through near center, with local load failure.

13

Figure 9 The deterioration of the underside of the specimen,

15

FORM NBS.n4A (1-71) U.S. DEPT. OF COMM. 1. PUBLICATION OR REPORT NO. 2. Gov't Accession

BIBLIOGRAPHIC DATA No. SHEET NBSIR 73-167

3. Recipient's Accession No.

4. TITLE AND SUBTITLE

i Fire Endurance Test of a Roof/Ceiling Construction

\ P o T" Hon ^\7P riTTlK Sin A fZvTlQ 1 iTn Ro^i

5. Publication Date

6. Performing Oiganizatioa Code

] 7. AUTHOR(S)

! Byung Chan Son

8. Performing Organization

NBSIR 73-167

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit No. 4600442

11. Contract/Grant No.

IAA-H-16-70

12. Sponsoring Organization Name and Address

Department of Housing and Urban Development

Washington, D.C. 20410

13. Type of Report & Period

Covered

Final

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

This is a revision of NBS-10405.

16. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here.)

In a program of evaluation of various housing systems proposed under Operation

BREAKTHROUGH, a fire endurance test was performed at the National Bureau of

Standards on a roof/ceiling assembly consisting of a paper honeycomb structural

core surfaced both sides with glass-fabric impregnated with polyester resin and

outer layers of gypsum board.

The test method was generally in accordance with the requirements of ASTM E 119,

Fire Tests of Building Construction and Materials, for loadbearing roof assemblies.

The applied load was 15.9 psf and the test results are valid only for roof /ceilings

of similar construction loaded at or below the stress level developed by this

loading.

Under a loading of 15.9 psf on a 13 ft. 5 in. span, which produced a stress

equivalent to the application of 20 psf on a 12 ft. span, failure occurred by

flame-through of the roof/ceiling assembly at 37 min. 13 sec.

17. KEY WORDS (Alphabetical order, separated by semicolons) Fire endurance; fire test; flame- through

failure, structural panel; glass-fabric reinforced plastic; housing Systems;

Operat ion BREAKTHROUGH; paper honeycomb; roof/ceiling assembly; structural panel

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